Some wearable articles are manufactured to include fastening members. For example, some varieties of diapers are manufactured with a pair of oppositely-oriented side fastening members, extending laterally from each side of a first waist region of the chassis, each fastening member having a fastener located at or near the outboard end thereof, and adapted to attach or adhere to a fastener receiving zone (“landing zone”) disposed on a second waist region of the chassis. The fastening members may be formed in part or in whole of a nonwoven web material. In some examples, the fastening members are formed at least in part of a laminate of one or more layers of nonwoven web material and one or more layers or strands of a polymeric elastic material, and fashioned and adapted in such a way as to be elastically extensible in at least the direction in which the fastening member is to be pulled during application and use. One type has fastening members extending from the rear waist region of the diaper, and is intended to enable the person applying the diaper (hereinafter, “applier”) to lay the diaper open on a surface, with the rear region of the diaper beneath a reclining wearer's bottom, wrap the chassis forward between the wearer's legs and up over the front of the lower torso, draw each fastening member from the rear waist region around a hip, and attach the end of each fastening member to the front region via the fastener, thereby forming a waistband and pant-like structure about the wearer. When the diaper is applied, each fastening member may be in direct contact with the wearer's skin at a hip.
In some examples of diapers having fastening members, it may be desirable that the fastening members be formed so as to cover substantial areas of skin at the wearer's hips. This may have two purposes, among others: First, comfort, resulting from distribution of normal force components of tension forces in the fastening members over greater, rather than lesser, areas of skin; and second, appearance.
It also may be desirable to form fastening members from material that is relatively soft to the touch, pliable and stretchy. Purposes for this may include comfort.
Fastening members may be subject to varying forces, resulting from tugging during application, and from the wearer's movements at the hips, particularly if the diaper is snugly applied. These forces may have various undesirable effects. A typical fastening member, e.g., one that extends from the rear waist region of a diaper, is longer at its inboard end than at its outboard end. This general geometry may be incorporated to allow for, e.g., better fit about the wearer's hips, and better distribution of lateral tension forces along a greater length along the location(s) where the fastening member joins the rear waist region, thereby reducing the likelihood of tearing along that line or locations proximate the inboard end of the fastening member. Conversely, a relatively shorter outboard end, typically having a fastener attached proximate thereto, allows for tugging by the applier by simply grasping between thumb and forefinger, and for easy selection and placement of a point or region of fastening, by simply placing the grasped, shortened outboard end at the desired location. This general geometry results in lateral tension forces being focused from a longer inboard region to a shorter outboard end region of the fastening member. This focusing, together with stretching, creates longitudinal force components within the fastening member.
Longitudinal force components acting within the fastening member may create the likelihood that portions of the fastening member such as a panel region and/or extensible zone thereof will undesirably laterally buckle and/or flip away from the wearer. For purposes of maximizing skin coverage for best appearance, evenly distributing forces, and wearer comfort, panel regions of fastening members may be formed so as to have the greatest length (in a longitudinal direction along the chassis) feasible under the circumstances. Increasing length adds to the area of the material forming the panel region. With increasing length and surface area of the panel region, undesirable buckling/flipping of the panel region material proximate either the top or bottom edges may be more likely, particularly when the wearer bends at the hips. This problem may be more likely to manifest itself in “tape” type fastening members, in which a comparatively short tab member, bearing a fastener and forming the end region of the fastening member, joins a relatively longer side panel region, such that a step-wise decrease in length of the fastening member exists where the panel region ends and the tab member extends therefrom. When the panel region and/or an extensible zone thereof is highly extensible (and relatively pliable), it may tend to buckle and flip about the relatively short tab member.
In examples in which a layer forming an end region of a fastening member is coextensive in length, or longer than, a layer of material forming the region immediately inboard of the end region, buckling/flipping of the panel region proximate its edges may be less likely because longitudinal force components resulting from lateral tension in the fastening member may be distributed into the end region. As a result, however, such longitudinal force components may act at or about the lateral edges of the fastener and contribute to causing the fastener to bend or “dish”, i.e., contribute to causing its lateral edges to be urged to turn up and away from the surface to which it is attached. For example, one type of diaper fastening member may include a fastener consisting of a patch of hooks, a component of a hook-and-loop fastening system (such as a 3M, APLIX or VELCRO hook-and-loop system). A patch of a corresponding loops component may be disposed at a landing zone on the outside front waist region of the diaper, so as to enable attachment when the hooks patch is pressed against the landing zone. Another example may have a fastener consisting of a patch of material bearing an adhesive effective to adhere to a smooth surface disposed at the landing zone. Upon being tugged laterally by an applier during application, and/or with lateral tension resulting from application and/or the wearer's movements, longitudinal force components of tension forces in the fastening member, acting at the edges of the fastener patch, can urge its longitudinally outer edges up and away from the landing zone, thereby causing a sub-optimal fastener attachment to the landing zone, or weakening the fastener's hold at the landing zone, or even causing the fastener's hold to fail—which may allow the diaper to come loose or fall free of the wearer.
In some circumstances, stresses in the fastening member resulting from lateral tension may concentrate in the end region near or at the inboard edges of the fastener zone. As a result, the likelihood of a tear beginning at the location of stress concentration is increased. For example, stresses may be concentrated at locations where the fastening member narrows to an end region, particularly if there is an abrupt structural discontinuity, such as created by the presence of, for example, the edge of a patch of a relatively stiffer material adhered to a substrate material. Tearing may occur in the end region, at or near the fastener zone, when the applier tugs on the fastening member to apply the diaper; or the end region may tear at or near the fastener zone from stresses resulting from the wearer's movements.
The above-described events, i.e., panel region buckling/flipping, fastener dishing, and tearing, may be deemed problematic because they may result in less than optimum performance and/or appearance, failure of the product, and consumer dissatisfaction.
Likelihood of the problems identified above may be decreased by the use of relatively more robust materials to form the fastening member. A material that is more robust, and therefore, stiffer and more resistive to buckling and tearing, may be used to form the panel region and/or extensible zone. Robustness of a material such as a stretch laminate can be increased, for example, by the use of materials having greater basis weights and/or densities. Similarly, increasing the bending stiffness of a fastener patch by selection of a thicker and/or denser patch material may make it more resistive to dishing.
These approaches, however, also may have undesirable consequences. If a fastener patch is too stiff and unyielding, when fastened at the wearer's waist it may feel like an unyielding object and be a source of discomfort for the wearer under certain circumstances. Increasing the strength of a stretch laminate may increase its stiffness, but decrease its extensibility and pliability, as well. Increasing the stiffness of a material that is against the wearer's skin in a region of the body subject to movement and bending may increase likelihood of discomfort for the wearer, and promote marking, irritation and chafing of the wearer's skin. For the manufacturer of disposable diapers, acceptable but relatively more robust materials may be relatively more expensive. If fastening members are not extensible, or not sufficiently so, then it may be necessary to build additional stretch features into, e.g., the waist regions of the chassis, if assurance of a comfortable and snug-fitting diaper is to be maintained.
From the foregoing it can be appreciated that the design of a fastening member involves a variety of concerns, and that a great number of variables and permutations in the combinations of materials, features and structures used is possible. Changing one material, feature or structure to address one concern may give rise to other concerns. A need for improvements in the combination of materials, features and structures used, that satisfactorily address and reduce concerns for comfort, performance and manufacturing cost of the fastening member and its associated wearable article, always exists.